Acute Appendicitis

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Chapter 335 Acute Appendicitis

John J. Aiken, Keith T. Oldham

Acute appendicitis, despite a declining incidence in the United States in the past half century, remains the most common acute surgical condition in children and a major cause of childhood morbidity. Approximately 80,000 children are affected annually in the United States, a rate of 4/1,000 children <14 yr of age. Although since the turn of the century there has been a trend toward shorter hospital stays, appendicitis accounts for >1 million hospital days utilized per year. Mortality is low, but morbidity remains high, mostly in association with perforated appendicitis.

The methods of diagnosis and treatment of appendicitis vary significantly among clinicians and hospitals, and consensus regarding a best practice approach to the child who presents with the chief complaint of abdominal pain and suspected appendicitis has been elusive. Management has changed substantially in the past several decades with improved antibiotics regimens, advances in imaging techniques, percutaneous drainage procedures by interventional radiologists, initial nonoperative management in selected cases, and the use of laparoscopy.

Pathology

Acute appendicitis is most likely a disease of multiple etiologies, the final common pathway of which involves invasion of the appendiceal wall by bacteria. One pathway to acute appendicitis begins with luminal obstruction; inspissated fecal material, lymphoid hyperplasia, ingested foreign body, parasites, and tumors have been implicated. Obstruction of the appendiceal lumen results in increasing intraluminal pressures from bacterial proliferation and continued secretion of mucus. Elevated intraluminal pressure, in turn, leads to lymphatic and venous congestion and edema followed by impaired arterial perfusion, eventually leading to ischemia of the wall of the appendix, bacterial invasion with inflammatory infiltrate of all layers of the appendiceal wall, and necrosis. This progression correlates with progression from simple appendicitis to gangrenous appendicitis and, thereafter, appendiceal perforation. Submucosal lymphoid follicles, which can obstruct the appendiceal lumen, are few at birth but multiply steadily during childhood, reaching a peak in number during the teen years, when acute appendicitis is most common, and declining after age 30 yr. Fecaliths and appendicitis are more common in developed countries with refined, low-fiber diets than in developing countries with a high-fiber diet; no causal relationship has been established between lack of dietary fiber and appendicitis.

The finding that <50% of specimens from cases of acute appendicitis demonstrate luminal obstruction on pathologic examination has prompted investigations of alternative etiologies. Enteric infection likely plays a role in many cases in association with mucosal ulceration and invasion of the appendiceal wall by bacteria. Bacteria such as Yersinia, Salmonella, and Shigella spp and viruses such as mumps, coxsackievirus B, and adenovirus have been implicated. In addition, case reports demonstrate the occurrence of appendicitis from ingested foreign bodies, in association with carcinoid tumors of the appendix or Ascaris and following blunt abdominal trauma. Children with cystic fibrosis have an increased incidence of appendicitis; the cause is believed to be the abnormal thickened mucus. Appendicitis in neonates is rare and warrants evaluation for cystic fibrosis and Hirschsprung disease.

A primary focus in the management of acute appendicitis is avoidance of sepsis and the infectious complications mostly seen in association with perforation. Bacteria can be cultured from the serosal surface of the appendix before microscopic or gross perforation and bacterial invasion of the mesenteric veins can result in portal vein sepsis (pylephlebitis) and liver abscess. Subsequent to perforation, the microbiologic fecal contamination may be localized to the right lower quadrant (RLQ) or pelvis by the omentum and adjacent loops of bowel, resulting in a localized abscess or inflammatory mass (phlegmon), or alternatively, the fecal contamination can spread throughout the peritoneal cavity, causing diffuse peritonitis. Young children typically have a poorly developed omentum and are often unable to control the local infection. Perforation and abscess formation with appendicitis can lead to fistula formation in adjacent organs, scrotal cellulitis and abscess through a patent processus vaginalis (congenital indirect inguinal hernia), or small bowel obstruction.

Clinical Features

Appendicitis is most common in older children, with peak incidence between the age of 12 and 18 yr; it is rare in children <5 yr of age (<5% of cases) and extremely rare (<1% of cases) in children <3 yr of age. It affects boys slightly more often than girls and whites more often than blacks in the United States. There is a seasonal peak incidence in autumn and spring. There appears to be a familial predisposition in some cases, particularly in children in whom appendicitis develops before age 6 yr.

Perforation is most common in young children, with rates as high as 82% for children <5 yr and approaching 100% in infants. There is an increased incidence of perforated appendicitis in children of minority race and children with Medicaid health insurance.

Appendicitis in children has an immensely broad spectrum of clinical presentation. The signs and symptoms can be classic or atypical and quite variable depending on the timing of presentation, the patient’s age, the position of the appendix, and individual variability in the evolution of the disease process. Children early in the disease process can appear well and have minimal symptoms, subtle findings on physical examination, and normal laboratory studies; those with perforation and advanced peritonitis often demonstrate bowel obstruction, renal failure, and septic shock.

Despite advances in imaging technology and computer-assisted decision-making models and scoring systems, accurate diagnosis can be difficult, and perforation rates have not changed in the past few decades.

Whereas the classic presentation of acute appendicitis is well described, this represents less than half the cases; therefore, most cases of appendicitis have an “atypical” presentation. The illness typically begins insidiously with generalized malaise and anorexia; the child does not appear ill and the family is not likely to seek consultation assuming the child has “stomach flu” or a viral syndrome. Unfortunately, if the diagnosis is appendicitis, the illness escalates rapidly with abdominal pain followed by vomiting; appendiceal perforation is likely to occur within 48 hr of the onset of illness, and the opportunity for diagnosis before perforation is generally brief.

Abdominal pain is consistently the primary and often the first symptom and begins shortly (hours) after the onset of illness. The pain is initially vague, unrelated to activity or position, often colicky, and periumbilical in location as a result of visceral inflammation from a distended appendix. Progression of the inflammatory process in the next 12-24 hr leads to involvement of the adjacent parietal peritoneal surfaces, resulting in somatic pain localized to the RLQ. The pain becomes steady and more severe and is exacerbated by movement. The child often describes marked discomfort with the “bumpy” car ride to the hospital, moves cautiously, and has difficulty getting onto the examining room stretcher. Nausea and vomiting occur in more than half the patients and usually follow the onset of abdominal pain by several hours. Anorexia is a classic and consistent finding in acute appendicitis, but occasionally, affected patients are hungry. Diarrhea and urinary symptoms are also common, particularly in cases of perforated appendicitis when there is likely inflammation near the rectum and possible abscess in the pelvis. Because enteric infections can cause appendicitis, diarrhea may be the initial manifestation and gastroenteritis may be the assumed diagnosis. In contrast to gastroenteritis, the abdominal pain in appendicitis is constant (not cramping or relieved by defecation), the emesis may become bile stained and persistent, and the clinical course worsens rather than improves over time. Fever is typically low-grade unless perforation has occurred. Most patients demonstrate at least mild tachycardia.

The temporal progression of symptoms from vague mild pain, malaise, and anorexia to severe localized pain, fever, and vomiting typically occurs rapidly, in 24-48 hr in the majority of cases. If the diagnosis is delayed beyond 36-48 hr, the perforation rate exceeds 65%. A period after perforation of lessened abdominal pain and acute symptoms has been described, presumably with the elimination of pressure within the appendix. If the omentum or adjacent intestine is able to wall off the infectious process, the evolution of illness is less predictable and delay in presentation is likely. If perforation leads to diffuse peritonitis, the child generally has escalating diffuse abdominal pain and rapid development of toxicity evidenced by dehydration and by signs of sepsis including hypotension, oliguria, acidosis, and high-grade fever. When several days have elapsed in the progression of appendicitis, patients often develop signs and symptoms of developing small bowel obstruction. If the appendix is retrocecal, appendicitis predictably evolves more slowly and patients are likely to relate 4-5 days of illness preceding evaluation. The pain is lateral and posterior and can mimic the symptoms associated with septic arthritis of the hip or a psoas muscle abscess.

Atypical clinical features include absence of fever, Rovsing sign, rebound pain, migration of pain, guarding, and anorexia in 30-50% of pediatric patients. Other atypical features include normal to increased bowel sounds and an abrupt onset of pain.

Physical Examination

The hallmark of diagnosing acute appendicitis remains a careful and thorough history and physical examination. A primary focus of the initial assessment is attention to the temporal evolution of the illness in relation to specific presenting signs and symptoms. In many children, appendicitis can be confidently diagnosed on clinical examination alone and they can thus be spared the treatment delay, expense, and possible radiation exposure associated with imaging studies.

Physical examination begins with inspection of the child’s demeanor as well as the appearance of the abdomen. Because appendicitis most often has an insidious onset, children rarely present <12 hr from the onset of illness, and the children who do present early are likely to have minimal findings. Children with early appendicitis (18-36 hr) typically appear mildly ill and move tentatively, hunched forward and often with a slight limp favoring the right side. Supine, they often lie quietly on their right side with their knees pulled up to relax the abdominal muscles, and when asked to lie flat or sit up, they move cautiously and might use a hand to protect the RLQ.

Early in appendicitis, the abdomen is typically flat; abdominal distention suggests more advanced disease characteristic of perforation or developing small bowel obstruction. Auscultation can reveal normal or hyperactive bowel sounds in early appendicitis, which are replaced by hypoactive bowel sounds as the disease progresses to perforation. The judicious use of morphine analgesia to relieve abdominal pain does not change diagnostic accuracy or interfere with surgical decision-making, and patients should receive adequate pain control.

Localized abdominal tenderness is the single most reliable finding in the diagnosis of acute appendicitis. In 1899, McBurney described the classic point of localized tenderness in acute appendicitis, which is the junction of the lateral and middle thirds of the line joining the right anterior-superior iliac spine and the umbilicus, but the tenderness can also localize to any of the aberrant locations of the appendix. Localized tenderness is a later and less-consistent finding when the appendix is retrocecal in position.

A gentle touch on the child’s arm at the beginning of the examination with the reassurance that the abdominal examination will be similarly gentle can help to establish trust and increase the chance for a reliable and reproducible examination. The examination is best initiated in the left lower abdomen, so that the immediate part of the exam is not uncomfortable, and conducted in a counterclockwise direction moving to the left upper abdomen, right upper abdomen, and lastly, the right lower abdomen. This should alleviate anxiety, allow relaxation of the abdominal musculature, and enhance trust. The examiner makes several “circles” of the abdomen with sequentially more pressure.

A consistent finding in acute appendicitis is rigidity of the overlying rectus muscle. This rigidity may be voluntary, to protect the area of tenderness from the examiner’s hand, or involuntary, secondary to peritonitis causing spasm of the overlying muscle. Physical examination findings must be interpreted relative to the temporal evolution of the illness. Abdominal tenderness may be vague or even absent early in the course of appendicitis and is often diffuse after rupture. Rebound tenderness and referred rebound tenderness (Rovsing sign) are also consistent findings in acute appendicitis but not always present. Rebound tenderness is elicited by deep palpation of the abdomen followed by the sudden release of the examining hand. This is often very painful to the child and has demonstrated poor correlation with peritonitis, so it should be avoided. Gentle finger percussion is a better test for peritoneal irritation. Similarly, digital rectal examination is uncomfortable and unlikely to contribute to the evaluation of appendicitis in most cases. Rectal exam may be helpful in selected cases, including when the diagnosis is in doubt, when a pelvic appendix or abscess is suspected, or in adolescent girls when ovarian pathology is suspected. Psoas and obturator internus signs are pain with passive stretch of these muscles. The psoas sign is elicited with active right thigh flexion or passive extension of the hip and typically positive in cases of a retrocecal appendix. The obturator sign is demonstrated by adductor pain after internal rotation of the flexed thigh and typically positive in cases of a pelvic appendix. Physical examination may demonstrate a mass in the RLQ representing an inflammatory phlegmon around the appendix or a localized abscess.

Diagnostic Studies

Laboratory Findings

A variety of laboratory tests have been used in the evaluation of children with suspected appendicitis. Individually, none are very sensitive or specific for appendicitis, but collectively they can affect the clinician’s level of suspicion and decision-making to proceed with pediatric surgery consultation, discharge, or imaging studies. Findings should be interpreted with attention to the temporal evolution of the illness.

A complete blood count with differential and urinalysis are commonly obtained.

The leukocyte count in early appendicitis (<24 hr of illness) may be normal and typically is mildly elevated with a left shift (11,000-16,000/mm³) as the illness progresses in the 1st 24-48 hr. Whereas a normal white blood cell count (WBC) never completely eliminates appendicitis, a count <8,000/mm³ in a patient with a history of illness >48 hr should be viewed as highly suspicious for an alternative diagnosis. The leukocyte count may be markedly elevated (>20,000/mm³) in perforated appendicitis and rarely in nonperforated cases; a markedly elevated WBC, other than in cases of advanced, perforated appendicitis, should raise suspicion of an alternative diagnosis.

Urinalysis often demonstrates a few white or red blood cells, due to proximity of the inflamed appendix to the ureter or bladder, but it should be free of bacteria. The urine is often concentrated and contains ketones from diminished oral intake and vomiting. Gross hematuria is uncommon and suggests primary renal pathology.

Electrolytes and liver chemistries are generally normal unless there has been a delay in diagnosis, leading to severe dehydration and/or sepsis. Amylase and liver enzymes are only helpful to exclude alternative diagnoses such as pancreatitis and cholecystitis and are not obtained if appendicitis is the strongly suspected diagnosis.

C-reactive protein increases in proportion to the degree of appendiceal inflammation but is nonspecific and not widely used. Serum amyloid A protein is consistently elevated in patients with acute appendicitis with a sensitivity and specificity of 86% and 83%, respectively.

The Pediatric Appendicitis score combines history, physical, and laboratory data to assist in the diagnosis (Table 335-1). Scores of ≤2 suggest a very low likelihood of appendicitis, while scores ≥8 are highly associated with appendicitis. Scores between 3 and 7 warrant further diagnostic studies. Nonetheless, no scoring system is perfectly sensitive or specific.

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